Activity of low mass stars in the light of spot signature in the Fourier domain

Abstract

Context. Magnetic fields exhibit a wide variety of behaviours in low mass stars and further characterization is required to understand these observations. Stellar photometry from space missions such as MOST, CoRoT, Kepler, and, in future PLATO, provide thousands of highly precise light curves (LC) that can shed new light upon stellar activity, in particular through the signature of transiting spots. Aims. We study the impact of star spots on light curves in the Fourier domain, reducing the degeneracies encountered by direct spot modelling in the temporal domain, and use this new formulation to explore the spot properties from the available data. Methods. We propose a model of LC power spectra at low frequency based on a description of spot transits that allows us to retrieve information about the amplitude of their photometric impact $\mathcal{H}$, and about the spot mean lifetime over the observation ${\tau }_{\mathrm{life}}$ when the power spectrum exibits rotation peaks. We first validate this method with simulated LCs and then apply it to the Kepler data to extract global trends over a set of more than 37 755 stars. Results. This analysis leads to a classification of the sample into "peakless" or "with peaks" spectra, and enables the identification of different activity regimes based on $\mathcal{H}$ and ${\tau }_{\mathrm{life}}$ for different ranges of Rossby number. More specifically, we observe an intense regime of activity between Ro = 0.7 and Ro = 1, for stars with masses under 1$M_{\odot }$. Conclusions. This new systematic method can be used to provide new observational constraints on stellar activity (and possibly a link with stellar magnetism) when applied to large photometric datasets, such as those from the future PLATO mission.

20 pages, 11 figures

References in corpus (11)

• CoRoT reveals a magnetic activity cycle in a Sun-like star
• Surface rotation and photometric activity for Kepler targets. II. G and F main-sequence stars, and cool subgiant stars
• Surface rotation of Kepler red giant stars
• Intrinsic photometric characterisation of stellar oscillations and granulation. Solar reference values and CoRoT response functions
• No Sun-like dynamo on the active star $\zeta$ Andromedae from starspot asymmetry
• The connection between stellar activity cycles and magnetic field topology
• Powering Stellar Magnetism: Energy Transfers in Cyclic Dynamos of Sun-like Stars
• Rotation Periods, Inclinations, and Obliquities of Cool Stars Hosting Directly Imaged Substellar Companions: Spin-Orbit Misalignments are Common
• Starspot signature on the light curve: Learning about the latitudinal distribution of spots
• Transition from multipolar to dipolar dynamos in stratified systems
• Kepler main-sequence solar-like stars: surface rotation and magnetic-activity evolution